The present invention relates to a color image processing apparatus which is peculiarly well fitted for an image processing apparatus such as a color copier in which a plain paper is used as a recording paper. The invention especially relates to a color image processing apparatus in which color ghost correction processing can be changed when a region is designated.
Furthermore, the invention relates to a color image processing apparatus having a partial color conversion function, to which the function to prevent a region designating color from becoming blurred is added to the color ghost correcting function.
In a color image processing apparatus such as a color copier in which laser beams are used, color image information is obtained by dissolving plural colors on a color document, and color images are recorded according to the color image information.
A color copier of this kind is designed and made so that it can conduct various image processing such as variable magnification processing and partial color conversion processing.
Partial color conversion processing means an image compiling process in which the color image information inside or outside the designated region can be recorded by the color used when the region is designated.
Designation of the region is usually conducted by a color marker. For instance, when the region a is designated by a blue marker as shown in FIG. 10A, the image within the region a is recorded by the color which was used to designate the region, wherein it is blue in this example. Refer to FIG. 10B.
If the image in another region needs to be erased, the images in the region can be recorded as black and white images.
In order to attain the partial color conversion mode, it is necessary to detect the color of a color marker used to designate the region, and the region itself. In order to boundaries for the region as shown in FIG. 11, the marker signals BP and RP are detected from the color marker which is formed across each scanning line (n, n+1, and so forth) and at the same time the region signals QB' and QR' are formed by the process.
According to these marker signals BP and RP, and the region signals QB' and QR', the images in the designated region are extracted and recorded and the recording processing shown in FIG. 10B is attained.
To change the subject slightly, there are color image processing apparatuses with a color ghost correcting function in addition to a partial color conversion function.
Color ghost is an unnecessary color signal which appears when an image signal is discriminated as plural color signals.
Namely, when a color image signal is discriminated, unnecessary color ghost appears in the peripheral area of black letters.
FIG. 12 shows an example of color ghost generation.
In this example, a Japanese letter " " (sei, gender) is picked up and color ghost generated after color separation is shown. This example depicts that the color ghost of red and blue appears at the edge of the black line, that of black appears at the edge of the blue line, and that of black appears at the edge of the red line, as shown in FIGS. 13A through 13C.
Other color combinations produce different color ghosts.
In many cases, the color ghost correction means is installed in apparatuses to obtain the object of reducing color ghosts and improving quality of recorded images.
When color ghost is corrected by this kind of color correction means, the color correction means sometimes misjudges the image information of a document when the partial color correction mode is selected.
When a specific region is painted out with a color marker as shown in FIG. 14 to record only the region, the contours 31, 32 of the image within the color marker become blurred.
The reasons are as follows.
For instance, if a red or blue marker exists around a black letter and the edge of the black letter is discriminated by a red or blue marker, the overlapped part is not discriminated as an image which is necessary for recording, even if it is an edge of the black letter.
The reason for that is because a color marker is only for detecting the region and a color marker portion is not recorded. That is the reason why the edges of images become blurred or narrow.
As explained above, color ghost correction has a special function to correct red and blue ghosts which appear around black letters. So, the peripheral part of a black letter is converted to white and the color conversion processing is not conducted.
The main object of the present invention is to solve these problems in a simple and cost-effective manner. The invention provides a color image processing apparatus which can prevent deterioration of image quality by changing the contents of color ghost correction when a specific color image is processed.
In a color image processing apparatus equipped with a partial color conversion function, the region of a color marker must be detected accurately as explained above. But the accuracy greatly depends on the manner in which the color is drawn.
Namely, when a color marker is drawn on a document correctly with high density, the color marker can be detected accurately. On the other hand, if a color marker becomes blurred in some places, then the color marker regions cannot be accurately detected.
When the output level of a CCD, which is quite often used to read images, is a little different, the color of a color marker and a black image overlap each other.
There are several methods to avoid this problem, such as adjusting the color marker region judging means or the blurred place correcting means. As a color marker can be detected accurately by applying these methods to the operation, false detection of the designated region caused by a blurred color marker or imbalance of the CCD level, can be eliminated.
But in the case when the region judging means is utilized, it becomes disadvantageously complicated. The region judging means is used to judge whether the information of the previous process should be used or not when a color marker becomes blurred, or even when a color marker becomes blurred, the region judging means should judge whether to neglect the information about several lines or several bits or not.
If blurred parts are needed to be corrected, an exclusive blurred part correcting means must be installed. Furthermore, it is necessary to process data in the blurred part correction means as well as in the region judging means. As a result, structure of the control circuit becomes complicated and it leads to high costs. It can be said to be a disadvantage.
Considering the circumstances, the second object of the present invention is as follows. A color image processing apparatus which has a color ghost correcting function in addition to a partial color conversion function, processes color marker blurred parts by appropriately utilizing the color ghost correction function.